The present invention relates to a magnetic head of the type which has a metal in a gap, called a Metal-In-Gap head.
A magnetic head used in magnetic storage having a large capacity is required to have a very small gap length and a small track width so as to provide a high density storage. A small gap length is, for example, 0.5 .mu.m or less. In addition, the coercive force of the storage medium has increased in recent years.
Accordingly, if a magnetic head having a small gap length and small track width is made of a magnetic oxide, such as ferrite, a sufficient magnetic flux density is not obtained, so that the magnetic conversion characteristics such as the overwrite characteristic, the time margin characteristic, the reproduction power and the like, are reduced.
On the other hand, it is difficult to manufacture the above described magnetic head of a metallic, magnetic material such as permalloy or sendust which provides a high saturation magnetic flux density, because of the difficulties in workability and low wear resistance.
Japanese Patent Application Laid-open 55-157121 discloses a Metal-In-Gap head (called hereinafter MIG head) in which a metallic, magnetic thin film is formed on the surfaces of the gap between a pair of ferrite cores so as to solve the above described problems.
FIG. 7 shows an example of the MIG head. The MIG head has a pair of ferrite cores 1 and 4. A metallic, magnetic thin layer 3 which has a higher saturation magnetic flux density than the core material is formed on a surface of the core 1. Between the thin layer 3 and the core 4, a gap layer 5 of nonmagnetic material is formed. Both cores 1 and 4 are joined by a glass joint 6. As for the metallic magnetic thin layer 3, sendust is preferable, because it has excellent magnetic characteristics and excellent heat resistance characteristics against the heat used in the glass joining operation.
However, a magnetic deteriorated layer 7 which deteriorates in coercive force and permeability is formed in the boundary zone between the ferrite core 1 and the thin layer 3. The layer 7 thus acts as a pseudo gap.
It is considered that the magnetic deterioration is caused by two reasons as described hereinafter.
The first is that the crystal structure of an initial layer of the sendust thin layer becomes irregular at the formation thereof. The second is that magnetically deteriorated substances are formed in the boundary zone by the thermal diffusion of components of ferrite and sendust, which is caused by the heat used in the glass joint is formed.
The magnetic deteriorated substances which are formed are, for example, oxides of aluminum in the sendust which is caused by oxygen in the ferrite. It is known that the thickness of the magnetic deteriorated layer 7 is about 0.2 .mu.m which is a considerable value compared with the gap length which is the thickness of the gap layer 5.
The pseudo gap formed by the deteriorated layer 7 produces a false reproduction output which is added to the reproduction output depending on the main gap, causing reproduction error.
As a method for preventing the influence of the pseudo gap, the interface between the ferrite and the sendust is so disposed as to make an angle with the gap forming surface (Japanese Patent Publication 63-8524).
This head prevents the influence of the pseudo gap through an azimuth loss. However, in order to provide such an interface, the sendust layer must be increased in thickness. In addition, although the error output is reduced, the head efficiency is not improved (IEEE TRANSACTIONS ON MAGNETICS, Vol. 24, No. 2, March, 1802-1804 (1988)).
Another method that has an intermediate layer such as permalloy disposed between sendust and ferrite is disclosed in Japanese Patent Applications Laid-open 63-91811 and 63-39106. However, the permalloy causes oxygen in the ferrite to diffuse at a temperature between 500.degree. C. and 750.degree. C. upon joining with glass at the manufacturing of the head, causing a reduction in magnetic characteristics of the sendust.